Method for heat dissipation on semiconductor device

ABSTRACT

A device and method wherein a thermo electric generator device is disposed between stacks of a multiple level device, or is provided on or under a die of a package and is conductively connected to the package. The thermo electric generator device is configured to generate a voltage by converting heat into electric power. The voltage which is generated by the thermo electric generator can be recycled back into the die itself, or to a higher-level unit in the system, even to a cooling fan.

RELATED APPLICATION/PRIORITY CLAIM

This application is a divisional of U.S. patent application Ser. No.10/930,590, filed on Aug. 31, 2004.

BACKGROUND

The present invention generally relates to heat dissipation with regardto semiconductor devices, and more specifically relates to a device andmethod of converting heat generated by a semiconductor device intoelectric power.

With the development of larger density, higher speed, multilevelmetallization, the problem of heat dissipation on semiconductor deviceshas become a significant problem. On multilevel dual damascene copperprocesses (or conventional multilevel Aluminum/Silicon) the number ofmetal-insulator stacks has increased to the point where convective heatdissipation is no longer effective and the devices will not functionproperly if the heat buildup is too great. For example, an Intel®Pentium 4 processor can have a requirement to dissipate from 75 to 100Watts at an operating temperature of 75-100 degree Celsius. In addition,the generation of the waste heat causes the unit to use more power, andpower that goes into heat does not improve device performance.

Presently, the common solution to this problem is to add fixed elementheat exchangers and cooling fans to the back of semiconductor devicepackages. In certain cases, failures have been documented clue tooverheating of the devices on an improperly cooled circuit board.

Existing solutions cause application packaging to be bulky and oversizedwith increased system complexity to incorporate the current methods toreduce the temperatures of the semiconductor packages.

OBJECTS AND SUMMARY

An object of an embodiment of the present invention is to provide adevice and method of converting heat generated by a semiconductor deviceinto electric power.

Another object of an embodiment of the present invention is to provide asolution to the problem of overheating of a semiconductor device whereinthe solution does not provide that the semiconductor device is bulky,oversized and overly complex.

Briefly, and in accordance with at least one of the foregoing objects,an embodiment of the present invention provides a device and methodwherein a thermo electric generator device is disposed between stacks ofa multiple level device. The electric generator device can be providedon or under a die of a package and conductively connected to thepackage. The thermo electric generator device is configured to generatea voltage by converting heat into electric power. The voltage which isgenerated by the thermo electric generator can be recycled back into thedie itself, or to a higher-level unit in the system, even to a coolingfan.

BRIEF DESCRIPTION OF THE DRAWINGS

The organization and manner of the structure and operation of theinvention, together with further objects and advantages thereof, maybest be understood by reference to the following description, taken inconnection with the accompanying drawings, wherein:

FIG. 1 illustrates an embodiment of the present invention wherein athermo electric generator device is provided between two layers of amultiple level device;

FIG. 2 illustrates an embodiment of the present invention wherein athermo electric generator device such as shown in FIG. 1 is provided ona die, connected to a package; and

FIG. 3 illustrates an embodiment of the present invention wherein athermo electric generator device such as shown in FIG. 1 is providedunder a die, connected to a package.

DESCRIPTION

While the invention may be susceptible to embodiment in different forms,there are shown in the drawings, and herein will be described in detail,specific embodiments of the invention. The present disclosure is to beconsidered an example of the principles of the invention, and is notintended to limit the invention to that which is illustrated anddescribed herein.

The present invention provides the incorporation of a thermo electricgenerator device 10 built right on a semiconductor device or itspackage. This device 10 can be, for example, sandwiched in between themiddle stacks of a multi-level device (as shown in FIG. 1), provided ona die 12 (as shown in FIG. 2) or provided between the die 12 and thepackage 14 (as shown in FIG. 3). Regardless, the thermo electricgenerating device 10 is configured to generate a voltage by convertingthe waste heat into electric power. As represented by line 16 in each ofFIGS. 1, 2 and 3, this voltage can be recycled by the system, hack intothe die itself, or to a higher-level unit in the system, even to acooling fan.

As shown in FIG. 1, thermo electric generation is based on the Seebeckprinciple where electrical energy is generated from temperaturedifferences between a hot reservoir (which may be one layer 18 of amulti-level device) and a cold reservoir (which may be another layer 20of a multi-level device), by connecting two materials to the hotreservoir and having them both terminate separately at the coldreservoir, if within the cold reservoir, the materials are connected toopposite ends of an electrical load, power will be generated asrepresented by voltage 22 in FIG. 1 (power is consumed at the hotreservoir and generated at the cold reservoir).

In FIG. 1, reference numeral 24 identifies electrical insulator, thermalconductor layers, reference numeral 26 identifies electrical conductor,thermal insulator layers, and reference numeral 28 identifies electricaland thermal insulation. Additionally, reference numeral 30 identifies ap-type material, and reference numeral 32 identifies an n-type material.Preferably, materials 30 and 32 are chosen to be p and n typesemiconductor materials, respectively, which have the high figures ofmerit, Z, wherein Z is defined as the ratio of the Seebeck coefficientto the product of the thermal and electrical resistivity: Z=α/(ρ*κ),where α=_Seebeck coefficient=ΔV/ΔT, ρ is the electrical resistivity, andκ is the thermal conductivity.

Preferably, the exact materials are chosen to maximize this value, whileminimizing cost. Because optimization of thermo-electric devicesinvolves minimizing the length of the p and n materials, they are wellsuited for incorporation into a semiconductor chip.

The amount of electrical power generated is dependent on the amount ofheat transferred from the hot reservoir (q_(h)) (i.e., layer 18 in FIG.1), which is at a temperature T_(h), and the efficiency of thethermo-electric generator, η.

The electrical power generated is equal to q_(h)*η.q _(h) =KΔT+α ² IT _(h)−0.5*RIwhere K is the overall heat conductivity of the materials;R is the overall electrical resistance of the materials;ΔT is the temperature difference between the hot and cold reservoirs,T_(h)−T_(c) (i.e., the temperature difference between layers 18 and 20in FIG. 1);I is the electrical current produced; andη is closely related to the Carnot efficiency, ΔT/T_(h).

A single thermo-electric generator of dimensions 1 cm²×0.1 cm thick,operating at T_(h)=100° C. and T_(c)=25° C., can easily produce anelectrical power output of 0.43 W with a thermal efficiency of 3.4%,using well-documented materials. In this case, q_(h), the heat inputinto the generator would be 12.36 W, increasing T_(h) would increaseq_(h) and the thermal efficiency. Stacking additional units on top ofeach other would additively increase the power output. Improvedmaterials would also improve the efficiency.

The thermo-electric cooling circuit 10 can be provided as aprefabricated layered structure, such as a laminate. This layeredstructure could be produced off-line and incorporated onto the die inthe final stages of fab or with the die in the package. It could beapplied to the top surface of the wafer as a part of the finalpassivation process. Then, the normal pad mask can be cut into thelayered structure after before pad mask. This could give improved heatremoval, from the top of the die, but not interfere with the normalinterconnect of the device. It would also permit masking andinterconnection to the thermo-electric cooling circuit at the same timeas the die.

The thermo electric generator can provide greater power density on thedie by more efficiently removing heat from the die, and possible by“recycling” the waste heat into power to be reused by the system.

The present invention may allow for a greater number of metal layers tobe added to devices for additional functionality. Additionally, smallerfinal products can be realized by the elimination of external coolingmethods now in use.

The several embodiments discussed, such as providing the thermo electricgenerator between the layers or on top of the device, can be utilized.More than one level of this heat removing material can also be used togive even greater removal of heat. For example, the layered structurecan be both below and on top of the die. This application can also beapplied to high power semiconductors or other MN technologies. Thiscould also be a part of the cavity that the die is placed on top (seeFIG. 3).

FIG. 2 illustrates an embodiment wherein the thermo electric generatordevice 10 is provided as a top layer, i.e., a layered structure on topof a die 12, wire bonded to the package 14 to remove the electric powergenerated by the thermo electric generator device 10. Lines 40 representthe normal wire bond from the die 12 to the package 14, while line 42represents wire bond from the thermo electric generator device 10 to thepackage 14. FIG. 3 is very similar to FIG. 2, but shows the situationwhere the thermo electric generator device 10 is under the die 12,rather than on top.

The present invention provides a device and method of converting heatgenerated by a semiconductor device into electric power. As such, thepresent invention provides a solution to the problem of overheating of asemiconductor device wherein the semiconductor device need not beprovided as being bulky, oversized and overly complex.

While embodiments of the present invention are shown and described, itis envisioned that those skilled in the art may devise variousmodifications of the present invention without departing from the spiritand scope of the appended claims.

What is claimed is:
 1. A method of converting heat into electric power,said method comprising: providing a thermoelectric generator devicewhich comprises: a top layer; a bottom layer; a first electricalconductor, thermal insulator layer in contact with said top layer; asecond electrical conductor, thermal insulator layer in contact withsaid bottom layer wherein both the first and second electricalconductor, thermal insulator layers are disposed between said top andbottom layers; a p-type material between the first and second electricalconductor, thermal insulator layers; an n-type material between thefirst and second electrical conductor, thermal insulator layers; and anelectrical and thermal insulating layer between the p-type material andthe n-type material, wherein a first end of said electrical and thermalinsulating layer between the p-type material and the n-type materialcontacts the first electrical conductor, thermal insulator layer anddoes not contact the top layer, and wherein a second end of saidelectrical and thermal insulating layer between the p-type material andthe n-type material contacts the second electrical conductor, thermalinsulator layer as well as the bottom layer, thereby providing anelectrical separation within the second electrical conductor, thermalinsulator layer, wherein each of said top and bottom layers comprise anelectrical insulator, thermal conductor layer which is non-electricallyconductively contactable with a device; and using said thermoelectricgenerator device to covert heat generated by the thermoelectricgenerator device into electric power.
 2. A method as recited in claim 1,further comprising providing that the bottom layer of the thermoelectricgenerator device is in contact with a die.
 3. A method as recited inclaim 1, further comprising providing that the top layer of thethermoelectric generator device is in contact with a die, and the bottomlayer of the thermoelectric generator device is in contact with apackage.
 4. A method as recited in claim 1, further comprisingsandwiching the thermoelectric generator device between two layers of amultiple layer device.